The present invention relates to new optically active compounds and liquid crystal compositions containing the compounds, and more particularly, the present invention relates to optically active 2,5-diphenyl pyrimidine derivatives, optically active liquid crystal compositions containing the derivatives and electro optical elements using the compositions.
Liquid crystal display elements are widely used as various display elements, such as watches, electronic calculators, television sets, computer ends, etc., because these elements have excellent characteristics, such as operativity at low voltage, minimized consumption of electric power, obtainability of thin display elements and so on.
At present, display elements of a twisted nematic (TN) type are widely used as liquid crystal display elements. However, the response of the display element is slower than that of a display element of light emitting type such as an electroluminescence display, a plasma display, and the like. Although improvement of the response time of the liquid crystal display has been tried in many ways, it shows no sign of marked improvement.
However, a new display method using a ferroelectric liquid crystal that has been studied has hope for the improvement of the response time. (Clark et al., Appl. Phys. Lett., 36, 899(1980)). This display method utilizes a ferroelectric chiral smectic C phase (abbreviated as S.sub.c * phase hereinafter) or other smectic phase such as a chiral smectic F, G, H or I phase, and the like. This method has a quick response time less than 1/100 to 1/1000 of that of the TN display method and a memory effect of bistability. It is expected to have wide application of a large sized television set of dynamic picture display, a high-speed light shutter, and the like.
However, in spite of these excellent characteristics, it is very difficult to find a compound having a preferable liquid crystal range for the chiral smectic liquid crystals different from the nematic liquid crystals which are used in the conventional TN type display method. Accordingly, compounds having a preferable liquid crystal range have been little known.
An object of the present invention is to provide optically active compounds having characteristics suited for the display method which is still being researched, especially having a preferable liquid crystal temperature range.